1. Field
The present invention relates to a storage device and a gain adjusting device that adjust a gain of an amplifier.
2. Description of the Related Art
In recent years, recording and reproducing a signal has been getting more difficult as the record density and data transfer speed of a storage device, such as a magnetic disc device, has been getting higher. Higher record density has lead to a demand for the higher track density (TPI: Tracks Per Inch) of a storage medium (magnetic disc) in its radial direction.
For this reason, such a Storage device carries out auto gain control (hereinafter “AGC”) on a reproduced signal read by a magnetic head when reading data out of a magnetic disc serving as a storage medium (see, e.g., Japanese Patent Application Laid-open No. 07-192238). AGC is carried out to control a gain of an amplifier amplifying a reproduced signal to keep the amplitude of the amplified signal constant.
A schematic description will be made of gain adjustment by conventional AGC, referring to FIG. 9. FIG. 9 is a timing chart for explaining response waveforms generated by conventional AGC. In FIG. 9, “SGATE” represents the timing at which servo information is read out of a recording medium by a head to carry out servo control.
“INPUT” represents the level (size or amplitude) of a servo information signal input from the head to a read channel at each SGATE timing. “SV AGC OUTPUT” represents the level of a gain signal (gain value) output from an AGC circuit to an amplifier (VGA) at each SGATE timing. “VGA OUTPUT” represents the level of an amplified servo information signal output from the amplifier at each SGATE timing.
As shown in FIG. 9, according to gain adjustment by conventional AGC, the AGC circuit loads a preset initial value or the last gain value (i.e., gain value converged in the last period) at the startup of SGATE to follow a change in “INPUT”.
The AGC circuit thus outputs a gain (“SV AGC OUTPUT”) following a change in “INPUT”, to the amplifier. As a result, “VGA OUTPUT” becomes constant as it approaches the latter half of SGATE.
Recently, for such a storage device, a technique of carrying out RRO (Repeatable Run-Out) correction using RRO information in servo control is adopted. Specifically, a postcode area is provided immediately after a servo area to record premeasured RRO information in the postcode area.
On data reproduction, RRO information is reproduced following the reproduction of servo information to carry out RRO correction using RRO information in servo control. This improves the on-track accuracy of a head.
When gain adjustment by AGC including RRO is carried out, to deal with data reproduction in the postcode area following the servo area, a method of keeping a change-following gain in the servo area and carrying out only the sample timing phase correction in the post code area to detect data is generally adopted. FIG. 10 is a timing chart for explaining response waveforms generated by conventional AGC including RRO. In FIG. 10, “SGATE” is the same as “SGATE” of FIG. 9.
“RROGATE”, on the other hand, represents the timing at which RRO information is read out of a recording medium by a head to carry out RRO correction. “INPUT” represents the levels (size or amplitude) of a servo information signal and an RRO information signal that are input from the head to a read channel at each SGATE timing and RROGATE timing.
“SV AGC OUTPUT” represents the level of a gain output from an AGC circuit to an amplifier at each SGATE timing and RROGATE timing. “VGA OUTPUT” represents the levels of an amplified servo information signal and an amplified RRO information signal that are output from the amplifier at each SGATE timing and RROGATE timing.
As shown in FIG. 10, according to gain adjustment by conventional AGC including RRO, the AGC circuit keeps a gain adopted in the servo area to output the gain to the amplifier at each RROGATE timing.
The above gain adjustment by AGC including conventional RRO, however, poses a problem of incapable of dealing with a change in a signal level in the postcode area.
Specifically, in the post code area, RRO information is measured as a magnetic head is kept on a track of a disc using the servo area already filled in with servo information, and the measured RRO information is written in. Because of this, the RRO information turns out to be different in recording condition (recording level) from the servo information.
As a result, as shown in FIG. 10, input of servo information and RRO information may become different in signal level from each other. In gain adjustment by AGC including conventional RRO, however, the AGC circuit keeps a gain adopted in the servo area at each RROGATE timing.
As a result, as shown in “VGA OUTPUT” in FIG. 10, the level of the amplified servo information signal becomes constant while the level of the amplified RRO information signal becomes not constant. This means that the conventional technique is incapable of dealing with a signal level change in the postcode area, which consequently leads to an inferior data detection rate.
In the postcode area, a preamble portion for taking in a gain or sample timing is reduced to improve recording density. This makes impossible ensuring a sufficient time for a gain to follow a change through a feedback loop. Such a circumstance also constitutes the cause of the inferior data detection rate.
There is the inferior data detection rate not only in the storage device having the post code area and the servo area, but also in such a storage device that following reproduction of first information, reproduces second information from a second area that is adjacent to a certain first area and that has the second information recorded at a recording level different from the recording level of the first information.